Explosives or blasting compositions of the aqueous gel or slurry type, commonly referred to as slurry explosives or blasting agents, and referred to herein as aqueous blasting compositions, have achieved wide acceptance as commercial blasting agents owing to their low cost, safety, physical properties and inherent water resistance. Such aqueous blasting compositions generally contain a continuous liquid phase, an inorganic oxidizing salt(s), usually predominately ammonium nitrate (AN), a thickening agent for the liquid phase in which some or all of the oxidizing salt is dissolved, a fuel and/or sensitizer and, optionally, other ingredients such as gassing and cross-linking agents. Of these ingredients, generally the fuel and/or sensitizer has the highest ingredient cost. Fine aluminum particles commonly are employed as both fuel and sensitizer in aqueous blasting compositions. Other fuels find substantial use as well, for example, liquid organic fuels, sulfur, carbonaceous materials, and others. Aluminum and certain other fuels or combinations thereof are relatively expensive, however.
U.S. Pat. No. 4,055,449 discloses the use of a relatively inexpensive immiscible liquid organic fuel which can be effectively dispersed throughout an aqueous blasting composition having a continuous aqueous phase and which dispersion can be stably maintained throughout the continuous phase by the use of a crystal habit modifier. That patent discloses that a crystal habit modifier will prevent loss of sensitivity that would otherwise occur due to the segregation or separation of oxidizer and fuel resulting from the coalescence of dispersed immiscible liquid fuel droplets. The crystal habit modifier induces the formation of a crystal matrix which prevents migration and coalescence of the liquid fuel droplets.
It has been found that some desensitization with time will occur in an aqueous blasting composition containing a continuous aqueous phase and an immiscible liquid organic fuel even in the presence of a crystal habit modifier, if a significant proportion of AN or other inorganic oxidizer salt is present in an undissolved, particulate form such as prills. This phenomenon is described in column 4 of U.S. Pat. No. 4,055,449. The crystal habit modifier functions well in controlling the crystal size of oxidizer salt crystals which may precipitate out of solution upon cooling of a composition from its elevated formulation temperature. However, the modifier cannot by itself effectively act on prills or particles that are not dissolved during formulation of the composition. And it is found that the presence of AN in large particle sizes such as prill form causes a loss of sensitivity with time. It has been found in the present invention that the addition of a nonionic surfactant to a composition containing a continuous aqueous, an immiscible liquid organic fuel dispersed throughout such phase, and a crystal habit modifier will retard desensitization that would otherwise occur due to the presence of the inorganic oxidizer salt particles.